Although gram-negative bacillemia has been a frequent and often fatal complication of the management of the immunologically "compromised host", there has been no comprehensive, prospective evaluation of serum immunoglobulins, opsonizing antibodies, bactericidal antibodies, class- specific antibody affinity, polymorphonuclear leukocyte function, and circulating bacterial antigens (particularly endotoxins) associated with onset of bacteremia in humans and the subsequent clinical events leading to death or survival. In the continuation of this study at the UCLA Medical Center, an additional tube of heparinized blood will be drawn each time a blood culture is obtained. Since approximately 7000 blood cultures are drawn per year and 250 gram-negative bacillemias are documented, stored plasma will become available from a large number of patients at the onset of gram-negative bacillemia. A variety of immunologic parameters can be assessed in relation to the clinical course of infection including heat-labile and heat-stable opsonins. Freshly drawn plasma will also serve as a source of leukocytes whose function can be assessed by a variety of tests of leukocyte phagocytic/bactericidal activity. Further, a new method is under development for detection of enterobacterial endotoxin by radioimmunoassay, which can also be performed on these same specimens. The results from this procedure will be compared to the limulus lysate gelation bioassay for endotoxin-like material. This study is likely to yield conclusive information on the incidence of gram-negative bacillemias which develop in the presence of opsonizing antibodies, bactericidal antibodies and altered leukocyte function, and as to whether multiple impairments in such host factors as well as circulating endotoxemia are directly related to morbidity and mortality. If serologic data derived from studies in this and other laboratories continue to support a protective role for antibody against "core" glycolipid antigens widely shared by enteric bacteria, immunization of human volunteers and high risk patients will be initiated in an attempt to control bacteremic infections caused by members of the family Enterobacteriaceae.